The present invention relates to GPS positioning, and more particularly the present invention relates to a method and system for processing GPS drifting.
GPS positioning, which is currently widely applied, has a positioning mechanism of determining a position using four satellites, including a 3-dimensional distance and a 1-dimensional time. Specifically, the GPS positioning technique leverages positions of three known points in the space and relative distances to the three points to calculate the position of a GPS receiver. In practical applications, positions of the three known points are provided by a satellite in the sky. The satellite runs accurately under ephemeris. A position of the satellite at a given moment is known. That is, the satellite emits a specific radio signal; the radio signal is received by the GPS receiver after propagation for a certain period. Since the radio propagation velocity is known, the relative distance from the GPS receiver to the satellite can be calculated from a difference between the time when the GPS receiver receives the signal and the time when the satellite emits the signal.
The accuracy of GPS positioning is about +/−10˜30 m. However, for a GPS application drifting is a common problem that affects the accuracy of GPS positioning. There are many causes behind GPS drifting, for example, position deviation of the satellite orbit, or ephemeris and clock error, all of which will lead to deviation in positioning accuracy. Furthermore, propagation of radio waves in the air will also be affected by lots of factors. When GPS signals pass through the atmosphere or ionosphere, the signal speed will change somewhat, which also causes GPS drifting.
It is known that various solutions for enhancing GPS accuracy have been proposed. For example, by using a position difference between a known position of a fixed station and a position indicated by a GPS system thereon, a position of a GPS receiver around the station is corrected. However, this solution is too expensive to be applied widely.
The Inertial Navigation System (INS) is also a system capable of providing a higher positioning accuracy. INS positioning is free of the influence of external electromagnetic interference, such that it has a high short-term data accuracy and a good stability. However, since navigation information is generated through integration, the positioning error will also increase with time; therefore, the long-term accuracy is bad. Besides, devices are usually very expensive. Therefore, INS is only equipped in high-end devices.